This proposal describes a 14 month multi-modality multi-site treatment study for a large sample (N=750 or more) of children with Attention Deficit Hyperactivity Disorder. Three different ADHD diagnostic groups ("Pure" ADHD; ADHD plus conduct/oppositional disorder; ADHD plus internalizing disorder) will be treated with psychostimulant medication and be randomized to one of three manualized psychosocial treatment groups. Standard Multimodal Treatment (SMMT), using a fixed set of interventions; Tailored Multimodal (TMMT), a program whose components are based on parental and school environment factors, and Placebo Multimodal Treatment (PMMT), which involves a non-specific, fixed, time- matched intervention. The aims of this project are: (1) To measure the effects of psychosocial and psychopharmacological treatments on the symptoms of ADHD (inattentive and hyperactive behaviors) and on social and academic functioning in a sample of ADHD children covering a wide demographic range, including minority and inner city children: (2) To measure the persistence of treatment effects on symptoms and impairment; (3) To measure the extent to which tolerance to medication develops during a 14 month treatment in children on medication and placebo psychosocial therapy, and whether the stimulant dosage requirements decrease following a 14 month active psychosocial therapy; (4) To measure the extent to which symptomatic and functional treatment outcome effects co- occur; (5) To estimate the cost-benefit of more or less tailored multi- modality therapies: (6) To examine the predictive validity of new ADD categories that will appear in DSM IV and ICD-10; (7) To determine the extent to which the psychiatric and cognitive profile of a patient, including comorbidity, predicts response to different types of multi- modality treatments; (8) to develop more appropriate treatment standards and measures that describe the components of school and home environment.